1. Field of the Invention
The present invention relates to drilling multiple wells from a single borehole, and in particular to separately drilling multiple offshore wells from a single conductor casing string set within a primary borehole.
2. Description of the Prior Art
Offshore platforms are both expensive to build and costly to operate. Recent trends to optimize production from offshore platforms are becoming evermore prevalent. Offshore platforms have limited space from which wells may be drilled and produced. Typically, a drilling deck, or well deck, for an offshore platform has a limited number of slots through which conductor casing strings extend for drilling and production. These conductor casing strings often extend several hundred feet to a sea floor, and then into a borehole which extends beneath the sea floor.
Prior art methods for drilling multiple wells from a single conductor casing string typically require expensive specialized equipment and downhole tools for drilling and producing multiple wells. This often provides for rather costly logistical requirements for transporting the specialized equipment and tools offshore, as well as rather costly drilling and completion operations, as compared to standard drilling operations for drilling only a single well through a singular conductor casing string. Additionally, the equipment which is used only for drilling, and which is not used in completion operations to become a permanent part of the well, has to be again transported by ocean going vessel when it is no longer required. This provides additional costs for transporting the equipment.